Amanda15
If you use Apple mobile devices, then you can use Airplay with your Roku devices.
https://support.roku.com/article/360057488733
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If you use Android, you may need an additional casting app from the Play Store. I use Web Video Caster. (WVC) You install the WVC app on your phone or mobile device from the Play Store, and then install the WVC receiver on your Roku device available from the Roku Channel Store. (or just search search for web video caster from your Roku device under "Streaming Channels"
https://channelstore.roku.com/details/dd37e6d096d3197a9578787890118e33/web-video-caster-receiver
https://channelstore.roku.com/en-ca/details/dd37e6d096d3197a9578787890118e33/web-video-caster-receiver (Canada Roku store)
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Web Video Caster will work on both Android and Apple devices. The free version is just fine (occasional ad on the phone), but they offer a one-time purchase for $3 or $4 that is ad-free and opens up all features. (bookmarks, etc).
In addition to Web Video Caster, you can also try using other casting apps like Castify or Tubio.
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Basically, with all the above apps, you just type in the web address where your content is located, and then you select which Roku device you want to cast to. (both the phone and the Roku device must be on the same network).
Feel free to post back if you have any additional questions.